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HTML
157 lines
6.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>生成更好的随机数</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.mt-rand" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">mt_rand</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">mt_rand</span> — <span class="dc-title">生成更好的随机数</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.mt-rand-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>mt_rand</strong></span>
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( <span class="methodparam">void</span>
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) : <span class="type">int</span></div>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>mt_rand</strong></span>
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( <span class="methodparam"><span class="type">int</span> <code class="parameter">$min</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$max</code></span>
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) : <span class="type">int</span></div>
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<p class="simpara">
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很多老的 libc
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的随机数发生器具有一些不确定和未知的特性而且很慢。PHP
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的 <span class="function"><a href="rand.html" class="function">rand()</a></span> 函数默认使用
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libc 随机数发生器。<span class="function"><strong>mt_rand()</strong></span>
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函数是非正式用来替换它的。该函数用了
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<a href="http://www.math.sci.hiroshima_u.ac.jp/~m_mat/MT/emt.html" class="link external">» Mersenne Twister</a>
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中已知的特性作为随机数发生器，它可以产生随机数值的平均速度比
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libc 提供的 rand() 快四倍。
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</p>
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<p class="simpara">
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如果没有提供可选参数 <code class="parameter">min</code> 和
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<code class="parameter">max</code>，<span class="function"><strong>mt_rand()</strong></span>
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返回 0 到 <span class="function"><a href="mt_getrandmax.html" class="function">mt_getrandmax()</a></span>
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之间的伪随机数。例如想要 5 到 15（包括 5 和 15）之间的随机数，用
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<em>mt_rand(5, 15)</em>。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.mt-rand-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">min</code></dt>
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<dd>
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<p class="para">
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可选的、返回的最小值（默认：0）
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</p>
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</dd>
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<dt>
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<code class="parameter">max</code></dt>
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<dd>
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<p class="para">
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可选的、返回的最大值（默认：<span class="function"><a href="mt_getrandmax.html" class="function">mt_getrandmax()</a></span>）
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.mt-rand-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回 <code class="parameter">min</code> （或者 0） 到 <code class="parameter">max</code> （或者是到 <span class="function"><a href="mt_getrandmax.html" class="function">mt_getrandmax()</a></span>
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，包含这个值）之间的随机整数。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.mt-rand-changelog">
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<h3 class="title">更新日志</h3>
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<p class="para">
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<table class="doctable informaltable">
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<thead>
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<tr>
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<th>版本</th>
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<th>说明</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr><td>4.2.0</td><td>随机数发生器自动进行播种。</td></tr>
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</tbody>
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</table>
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.mt-rand-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-4135">
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<p><strong>Example #1 <span class="function"><strong>mt_rand()</strong></span> 例子</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">() . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">() . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">(</span><span style="color: #0000BB">5</span><span style="color: #007700">, </span><span style="color: #0000BB">15</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程的输出类似于：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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1604716014
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1478613278
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6
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</pre></div>
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</div>
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</div>
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</p>
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</div>
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<div class="refsect1 notes" id="refsect1-function.mt-rand-notes">
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<h3 class="title">注释</h3>
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<div class="caution"><strong class="caution">Caution</strong>
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<p class="para">
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The distribution of <span class="function"><strong>mt_rand()</strong></span> return values is biased
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towards even numbers on 64-bit builds of PHP when
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<code class="parameter">max</code> is beyond <em>2^32</em>.
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</p>
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</div>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.mt-rand-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="mt_srand.html" class="function" rel="rdfs-seeAlso">mt_srand()</a> - 播下一个更好的随机数发生器种子</span></li>
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<li class="member"><span class="function"><a href="mt_getrandmax.html" class="function" rel="rdfs-seeAlso">mt_getrandmax()</a> - 显示随机数的最大可能值</span></li>
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<li class="member"><span class="function"><a href="rand.html" class="function" rel="rdfs-seeAlso">rand()</a> - 产生一个随机整数</span></li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |